The Journal of Arthroplasty xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Postoperative Coronal Alignment After Total Knee Arthroplasty: Does Tailoring the Femoral Valgus Cut Angle Really Matter? Jason A. Davis, MD a, Craig Hogan, MD b, Michael Dayton, MD b a b
Ellis County Orthopaedics, HealthTexas Provider Network/Baylor Scott & White Health, Waxahachie, TX Department of Orthopedics, University of Colorado School of Medicine, Academic Office One, Aurora, CO
a r t i c l e
i n f o
Article history: Received 17 October 2014 Accepted 7 March 2015 Available online xxxx Keywords: Postoperative coronal alignment hip-to-ankle radiographs valgus cut angle total knee arthroplasty mechanical femorotibial angle
a b s t r a c t Postoperative alignment was measured in 80 TKA divided into 2 groups. Knees in the tailored group (n = 40) were performed with a personalized valgus cut angle (VCA) based on preoperative hip-to-ankle (HTA) radiographs. The fixed group knees (n = 40) were performed utilizing a 4° VCA in valgus knees and obese patients, and 5° in neutral and varus knees. There was no significant difference between groups in average preoperative mechanical alignment or average severity of preoperative deformity. There was no statistically significant difference between groups in postoperative mechanical alignment (tailored: 2.6°; fixed: 1.3°; P = 0.08) or severity of residual deformity (tailored: 3.5°; fixed: 2.6°; P = 0.10). Accuracy of the tibial cut angle (TCA) and severity of the preoperative deformity were strong independent predictors of postoperative alignment (R2 = 58% and R2 = 33%, respectively). © 2015 Elsevier Inc. All rights reserved.
Background In addition to soft tissue balancing and stable component fixation, implant alignment is arguably the most important technical factor for successful outcome and longevity in total knee arthroplasty (TKA) [1–5]. Many studies have implicated component malalignment in the failure of TKA through polyethylene wear and loosening [1,6–11]. Despite recent data challenging the ideal postoperative coronal alignment of the lower extremity [12–14], the most commonly accepted goal is to achieve a mechanical femorotibial (MFT) angle within + 3° of neutral such that the mechanical axis passes through the center of the knee in the coronal plane in effort to disperse forces across the implants in an even distribution. This is achieved by making coronal bone cuts perpendicular to the mechanical axes of the femur and tibia [1,3,5,8,11]. In regard to the femur, this cut is often referenced from the anatomic axis of the femur utilizing a corrective valgus cut angle (VCA) as there is a disparity between the mechanical and anatomic axes ranging from 2° to 9° with a mean of 5° to 6° along with some reported morphologic and gender variation [15–17]. Standard practice for many surgeons is to use the same VCA, typically 5° or 6°, for all patients with disregard for any variation in the femoral mechanical One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2015.03.013. The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2015.03.013. Reprint requests: Jason A. Davis, MD, Ellis County Orthopaedics, 2460 N. I-35 East, Ste. 225, Waxahachie, TX 75165.
anatomic (FMA) angle within the population. On the other hand, some surgeons tailor the intraoperative VCA based on preoperative standing hip-to-ankle (HTA) anteroposterior radiographs (Fig. 1), which have been shown to allow accurate measurement of alignment with strong interobserver and intraobserver reliability [18,19]. Controversy exists as to whether acceptable coronal mechanical alignment can be achieved by utilizing a standardized distal femoral VCA of 4° to 7° instead of a patient-specific VCA based on the FMA angle measured on preoperative HTA radiographs. The purpose of this study was to assess whether there is any significant difference in postoperative alignment between these 2 approaches by retrospectively comparing TKA performed by 2 surgeons who adhere to one or the other philosophy. We hypothesized that there would be no significant difference in the postoperative MFT angle or in the number of limbs that achieved alignment within + 3° of neutral with either approach in uncomplicated primary TKA. Materials & Methods After approval from the institutional review board, we performed a retrospective review of 80 primary TKA with appropriate radiographic records performed at a single academic institution from January 2013 to January 2014 by 1 of 2 fellowship trained total joint surgeons or by a fellow or resident under their direct supervision. All patients underwent cemented, posterior stabilized TKA. Patients were divided into 2 groups based upon which surgeon performed the procedure. Both surgeons utilize an intramedullary femoral guide for establishing the distal femoral cut, and an extramedullary guide to establish the tibial cut. The senior author utilizes gap balanced resection and determines the femoral VCA based on preoperative measurement on HTA
http://dx.doi.org/10.1016/j.arth.2015.03.013 0883-5403/© 2015 Elsevier Inc. All rights reserved.
Please cite this article as: Davis JA, et al, Postoperative Coronal Alignment After Total Knee Arthroplasty: Does Tailoring the Femoral Valgus Cut Angle Really Matter?, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.03.013
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J.A. Davis et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx
institution by a single investigator (JD). All measurements were obtained from standing HTA radiographs. Preoperative alignment was determined by measuring the angle between a line extending from the center of the femoral head to the deepest part of the trochlea of the distal femur, and a line extending from the center of the proximal tibia as the midpoint between the tibial eminences to the center of the talus. Postoperative alignment was assessed by measuring the angle between a line extending from the center of the femoral head to the center of the cam and post articulation, and a line from the same to the center of the talus (Fig. 2). Each alignment measurement was performed 3 times by the same investigator with positive values representing varus alignment and negative values representing valgus alignment. Similarly, the angle of the tibial cut (TCA) was obtained by a single measurement utilizing a line from the center of the talus to the center of the tibial baseplate, and a line parallel to the tibial baseplate (Fig. 3).
Fig. 1. Determining the valgus cut angle (VCA) is performed by (A) identifying the femoral mechanical anatomic (FMA) angle formed by the angle between the anatomic axis of the femur (AAF) and the mechanical axis of the femur (MAF), then (B) applying the FMA angle to the perpendicular axis of the AAF.
radiographs (tailored group, n = 40). Tailored group knees were implanted with either the Journey II (Smith & Nephew, Inc., Andover, MA; n = 34) or the Sigma RP (Depuy,Warsaw, IN; n=6). Conversely, fixed group patients (n = 40) were performed by a surgeon who utilizes a measured resection and does not rely on preoperative HTA radiographic measurements to set the VCA. Rather, a fixed VCA of 5° is utilized for neutral or varus knees, and 4° is utilized for valgus knees or in obese patients with large medial thigh folds in an effort to avoid irritation during gait postoperatively. Knees in the fixed group were implanted with either the PFC Sigma (Depuy, Warsaw, IN; n=29) or the Attune (Depuy, Warsaw, IN; n = 11). Exclusion criteria were patients who underwent revision total knee arthroplasty, patients in the tailored group who did not have preoperative HTA films indicating that the VCA could not have been personalized, and patients who lacked postoperative HTA radiographs. Preoperative and postoperative mechanical alignment (MFT angle) as well as the angle of the tibial cut in each group were measured utilizing the digital PACS software (McKesson Radiology Station Lite) at our
Fig. 2. Preoperative and postoperative alignment of the lower limb is obtained by measuring the mechanical femorotibial (MFT) angle in (A) a preoperative hip-to-ankle (HTA) radiograph as the angle between the mechanical axis of the femur (MAF) and the mechanical axis of the tibia (MAT), and in (B) a postoperative HTA radiograph, respectively.
Please cite this article as: Davis JA, et al, Postoperative Coronal Alignment After Total Knee Arthroplasty: Does Tailoring the Femoral Valgus Cut Angle Really Matter?, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.03.013
J.A. Davis et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx
Fig. 3. The tibial cut angle (TCA) is measured by the angle between a line extending from the center of the tibial base plate to the center of the talus and a line parallel to the base plate. In this example, the angle is 91.8° or 1.8° of valgus.
Other data such as height, weight, body mass index (BMI) and type of implants were collected from the patients’ electronic medical records (preoperative history and physical notes and operative notes). Statistical Analysis The primary outcome measure was postoperative alignment. Two common transformations, the absolute value of the angle and an indicator for whether the angle was within + 3° of neutral, were also evaluated. Differences in continuous variables between the fixed and tailored groups were evaluated using 2-group t tests. A chi-square test for difference in proportions was used to estimate between-group differences in binary variables. Simple linear regression was used to evaluate the association between postoperative alignment (MFT angle) and preoperative alignment (MFT angle) and the association between postoperative alignment (MFT angle) and TCA. Multiple regression was used to estimate the combined effect of TCA and preoperative alignment. Intraobserver reliability was assessed using the intra-class correlation coefficient (ICC) by utilizing the Strout-Fleiss reliability statistic for repeated measurements. All analyses were done with SAS v9.3 (SAS Institute, Inc., Cary, NC). Results Intraobserver reliability showed a high level of repeatability in the measurement of preoperative and postoperative MFT angles on HTA radiographs. The ICC was 0.90 preoperatively and 0.96 postoperatively.
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There were no significant differences between study groups in regard to height, weight, BMI, average preoperative alignment or severity of deformity. Preoperative HTA radiographs were not available in 5 of the 40 patients in the fixed group. The average preoperative alignment (MFT angle) in the tailored group was 4.6° and the average MFT angle in the fixed group was 3.8° (P = 0.65). The average severity of deformity extrapolated by utilizing the absolute value of the MFT angle (representing the degrees deviation from neutral) was 6.9° in the tailored group and 7.2° in the fixed group (P = 0.75) (Table 1). The only difference between surgeons involved the TCA. The mean TCA in the fixed group was closer to 0°, averaging −0.6°, compared to 1.2° in the tailored group (P b 0.001). However, there was no significant difference between groups in the mean of the absolute values of the TCA (tailored: 1.9°; fixed: 1.8°; P = 0.70), a stronger indicator for the accuracy of the tibial cut (Table 2). Postoperatively, there were no statistically significant differences between study groups in alignment, severity of residual deformity, or the number of knees within + 3° of neutral. Given 40 knees per group, a difference of 1.5 in the average postoperative angle would have been significant at the 0.05 level; this difference is substantially less than 3̊, a difference that would be considered a clinically meaningful difference. The tailored group had an average postoperative alignment (MFT angle) of 2.6° and the fixed group had an average of 1.3° (P = 0.08). The tailored group had an average severity of residual deformity of 3.5° compared to 2.6° in the fixed group (P = 0.10). Twenty-two knees in the tailored group and 27 knees in the fixed group had postoperative MFT angles within + 3° (P = 0.25) (Table 2). Both the preoperative MFT angle (R2 = 33%) and TCA (R 2 = 58%) were independent predictors for postoperative alignment (MFT angle), and the preoperative severity of deformity (defined by the mean of the absolute values of the MFT angle) and accuracy of the TCA (defined by mean of the absolute values of the TCA) were independent variables impacting the postoperative residual deformity (defined by mean of the absolute values of the postoperative MFT angle). The strongest independent predictor was the TCA, and when combined with the preoperative MFT angle in a regression model, the R2 improved significantly (R2 = 66%). Discussion Currently, there is limited and conflicting data in the literature to determine whether there is an advantage in tailoring the VCA to each patient’s preoperative HTA radiograph. In a radiographic study of preoperative HTA radiographs by Bardakos et al, the VCA in 174 knees undergoing TKA was measured and determined that as many as 51% of patients required a VCA less than 5° or greater than 6° to achieve neutral alignment. The authors concluded that mechanical axis cannot be consistently restored utilizing a fixed VCA for all patients [15]. In a similar retrospective study of preoperative CT scout films of osteoarthritic knees in 83 patients, Kharwadkar et al found that the average VCA was 5.4°. Although the authors concluded that routine use of 5° or 6° for VCA is safe for uncomplicated primary TKA, Bardakos et al points out that despite leading to acceptable alignment on average,
Table 1 Preoperative Patient Indices as Mean. Tailored Group n Height (cm) Weight (kg) BMI (kg/m2) MFT angle (°) (ABS) MFT angle (°)
40 166 + 9.8 83.1 + 18.7 30.3 + 6.3 4.6 + 6.7 6.9 + 4.2
Fixed Group
P
a
40 170 + 11.1 85.0 + 21.9 29.3 + 5.3 3.8 + 8.1 7.2 + 5.2
0.10 0.69 0.41 0.65 0.75
BMI = body mass index, MFT angle = mechanical femorotibial angle, ABS = absolute value. Data are presented as mean + SD. a Preoperative radiographs were not available in 5 patients.
Please cite this article as: Davis JA, et al, Postoperative Coronal Alignment After Total Knee Arthroplasty: Does Tailoring the Femoral Valgus Cut Angle Really Matter?, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.03.013
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J.A. Davis et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx
Table 2 Postoperative Radiographic Measurements as Mean.
n TCA (°) (ABS) TCA (°) MFT angle (°) (ABS) MFT angle (°) MFT angle + 3°
Tailored Group
Fixed Group
P
40 1.2 + 2.1 1.9 + 1.5 2.6 + 3.4 3.5 + 2.7 22 (55%)
40 −0.6 + 2.1 1.8 + 1.2 1.3 + 3.2 2.6 + 1.9 27 (68%)
b0.001 0.70 0.08 0.10 0.25
TCA = tibial cut angle, ABS = absolute value, MFT angle = mechanical femorotibial angle. Data are presented as mean + SD or N (%).
the data suggests 42% of the knees in the aforementioned study fell outside the 5° to 6° range; thus, a routine cut of 5° or 6° may lead to inaccuracy in a significant percentage of knees [15,20]. On the other hand, in 124 primary TKA, the use of preoperative HTA radiographs and a tailored VCA compared to a fixed 5° VCA failed to show a significant difference in the postoperative mechanical alignment in a single-surgeon, prospective randomized study by McGrory et al when using the central 1/3 of the knee to define neutral alignment. There was also no difference between groups in postoperative mechanical alignment by average distance from neutral. Patients with previous hip or ankle surgery, femoral or tibial fracture, deformity of 15° or greater, or those with a BMI N 40 kg/m2 were excluded [21]. Most recently, Deakin and Sarungi published a single-surgeon retrospective cohort study of 124 knees performed with a fixed 7° VCA compared to 87 knees performed with a variable VCA based on preoperative HTA radiographs. Eighty-five percent of knees in the variable group had postoperative alignment within + 3° of neutral compared to 69% in the fixed angle group, a statistically significant difference (P = 0.006). The authors concluded that a fixed VCA is inappropriate and that tailoring the VCA to the patient’s specific anatomy can improve postoperative alignment [19]. It should be noted that the importance of obtaining a mechanical axis within + 3° of neutral has recently been called into question. Parrette et al published the results of a 15 year retrospective survivalship study of 398 knees. In the so called mechanically aligned group of 292 knees, there were 45 (15.4%) revisions compared to 14 (13%) of the 106 knees with mechanical alignment outside + 3° of neutral (P = 0.88). Seventeen (5.8%) of the 292 implants in the mechanically aligned group were revised for aseptic loosening, mechanical failure, or wear, compared to 4 (3.8%) of the 106 implants outside the acceptable range (P = 0.49). The authors concluded that postoperative mechanical alignment of 0° + 3° did not improve 15 year survival and showed little predictive value [12]. In a different 15 year follow-up study, Bonner et al showed similar results, although the authors do mention a statistically insignificant trend that favors knees that are more accurately aligned [13]. Furthermore, the concept of so called “constitutional varus” has been demonstrated by Bellemens et al in the normal population, and the authors suggest that a neutrally aligned total knee implant for these individuals may not be natural or desirable [14]. Despite these recent challenges, achieving a neutral alignment after TKA is the most widely accepted surgical goal emphasized in the literature. In this study, we demonstrated that there was no statistically significant difference, and more importantly, no clinically meaningful difference, in postoperative mechanical alignment between TKA performed by a surgeon who customizes the VCA based on the FMA angle measured on preoperative HTA radiographs, compared to a surgeon who utilizes a standardized VCA of 4° for valgus knees and obese patients, and 5° for neutral or varus knees. The results were consistent across 3 commonly utilized methods in the literature: evaluating the mean alignment where varus and valgus are designated with a + or − value; evaluating the mean of the absolute values of alignment to demonstrate the mean distance from neutral, or in other words, the average severity of the coronal plane deformity; and presenting the number of knees that fall within or outside the generally accepted + 3° of
neutral [4]. The results also demonstrate that the accuracy of the tibial cut (TCA) and the severity of the preoperative deformity (MFT angle) are strong independent predictors of postoperative alignment. Thus, the importance of achieving an accurate tibial cut perpendicular to the mechanical axis of the tibia becomes significantly more important as the severity of the preoperative deformity increases. The current study has a number of limitations. Due to the retrospective nature of this study, there were several patients not included in the study due to incomplete radiographic records. Also, there was no standardized protocol which introduces subjectivity in establishing the VCA as well as selection bias. Furthermore, the study groups were defined by 2 different surgeons, each with trainee involvement, which introduces several potentially confounding factors. First, the differences in skill and intricacies in surgical approach are not standardized to each group. However, despite a gap balanced versus measured resection, both surgeons perform the distal femoral and proximal tibial cuts in like fashion with an intramedullary femoral guide and an extramedullary tibial guide, respectively. Thus, whether a gap balanced or measured resection was utilized, there should have been no bearing on establishment of the coronal alignment in extension between surgeons. In addition, the fact that multiple implant systems were used in each group raises the question of whether disparities exist between the instrumentation and what effect that may have on the accuracy, consistency and orientation of both the distal femoral and proximal tibial cuts. Although the current study was not designed to evaluate this variable, in the small sample available there was no evidence that choice of instrumentation made an impact on postoperative coronal alignment. Nevertheless, a prospective, randomized, single-surgeon, singleimplant study would be the optimal design to eliminate these potentially confounding factors for future studies. Other limitations to consider are those associated with the assumption of HTA radiographs as an accurate representation of true alignment. It has been demonstrated that with 40° of limb rotation, the femoral mechanical anatomic (FMA) angle can vary by 1° to 2.5° and the limb alignment (MFT angle) can vary up to 5° [22,23]. Thus, without a standardized protocol for obtaining HTA (same stance, limb rotation, distance from x-ray source, technician, etc.), there is risk for error. Conclusions Despite the limitations of this study, our data suggest that when performing an uncomplicated primary total knee arthroplasty, utilizing a standardized VCA of 4° for valgus knees and 5° for neutral or varus knees can lead to acceptable postoperative alignment. The severity of the preoperative coronal deformity and the accuracy of the tibial cut are strongly correlated to postoperative alignment, and imply that achieving a tibial cut perpendicular to the mechanical axis of the tibia becomes particularly more important as the severity of the preoperative varus or valgus deformity increases. Acknowledgments The authors thank Pamela Wolfe, PhD, for her time, effort, and expert statistical analyses. The authors affirm there was no outside funding or industry influence for this study. References 1. Jeffery RS, Morris RW, Denham RA. Coronal alignment after total knee replacement. J Bone Joint Surg (Br) 1991;73(5):709. 2. Matsuda S, Kawahara S, Okazaki K, et al. Postoperative alignment and ROM affect patient satisfaction after TKA knee. Clin Orthop Relat Res 2013;471(1):127. 3. Longstaff LM, Sloan K, Stamp N, et al. Good alignment after total knee arthroplasty leads to faster rehabilitation and better function. J Arthroplasty 2009;24(4):570. 4. Rebal BA, Babatunde OM, Lee JH, et al. Imageless computer navigation in total knee arthroplasty provides superior short term functional outcomes: a meta-analysis. J Arthroplasty 2014;29(5):938.
Please cite this article as: Davis JA, et al, Postoperative Coronal Alignment After Total Knee Arthroplasty: Does Tailoring the Femoral Valgus Cut Angle Really Matter?, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.03.013
J.A. Davis et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx 5. Choong PF, Dowsey MM, Stoney JD. Does accurate anatomical alignment result in better function and quality of life? Comparing conventional and computer-assisted total knee arthroplasty. J Arthroplasty 2009;24(4):560. 6. Bargren JH, Blaha JD, Freeman MAR. Alignment in total knee arthroplasty: correlated biomechanical and clinical observations. Clin Orthop 1983;173:178. 7. Fang D, Ritter M, Davis K. Coronal alignment in total knee arthroplasty: just how important is it? J Arthroplasty 2009;24:39. 8. Ritter MA, Faris PM, Keating EM, et al. Post-operative alignment of total knee replacements: its effect on survival. Clin Orthop 1994;299:153. 9. Sharkey PF, Hozack WJ, Rothman RH, et al. Why are total knee arthroplasties failing today? Clin Orthop 2002;404:7. 10. Werner FW, Ayers DC, Maletsky LP, et al. The effect of valgus/varus malalignment on load distribution in total knee replacements. J Biomech 2005;38:349. 11. Berend ME, Ritter MA, Meding JB, et al. Tibial component failure mechanisms in total knee arthroplasty. Clin Orthop Relat Res 2004;428:26. 12. Paratte S, Pagnano MW, Trousdale RT, et al. Effect of postoperative mechanical axis alignment on the fifteen-year survival of modern, cemented total knee replacements. J Bone Joint Surg Am 2010;92(12):2143. 13. Bonner TJ, Eardley WG, Patterson P, et al. The effect of post-operative mechanical axis alignment on the survival of primary total knee replacements after a follow-up of 15 years. J Bone Joint Surg (Br) 2011;93(9):1217. 14. Bellemans J, Colyn W, Vandenneucker H, et al. The Chitranjan Ranawat award: is neutral mechanical alignment normal for all patients? The concept of constitutional varus. Clin Orthop Relat Res 2012;470(1):45.
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15. Bardakos N, Cil A, Thompson B, et al. Mechanical axis cannot be restored in total knee arthroplasty with a fixed valgus resection angle: a radiographic study. J Arthroplasty 2007;22(6 Suppl. 2):85. 16. Deakin AH, Basanagoudar PL, Nunag P, et al. Natural distribution of the femoral mechanical-anatomical angle in an osteoarthritic population and its relevance to total knee arthroplasty. Knee 2012;19(2):120. 17. Wang Y, Zeng Y, Dai K, et al. Normal lower-extremity alignment parameters in healthy Southern Chinese adults as a guide in total knee arthroplasty. J Arthroplasty 2010;25(4):563. 18. Skytta ET, Haapamaki V, Koivikko M, et al. Reliability of the hip-to-ankle radiograph in determining the knee and implant alignment after total knee arthroplasty. Acta Orthop Belg 2011;77(3):329. 19. Deakin AH, Sarungi M. A comparison of variable angle versus fixed angle distal femoral resection in primary total knee arthroplasty. J Arthroplasty 2014;29(6): 1133. 20. Kharwadkar N, Kent RE, Sharara KH, et al. 5° to 6° of distal femoral cut for uncomplicated primary total knee arthroplasty: is it safe? Knee 2006;13(1):57. 21. McGrory JE, Trousdale RT, Pagnano MW, et al. Preoperative hip to ankle radiographs in total knee arthroplasty. Clin Orthop Relat Res 2002;404:196. 22. Jiang CC, Insall JN. Effect of rotation on the axial alignment of the femur. Pitfalls in the use of femoral intramedullary guides in total knee arthroplasty. Clin Orthop Relat Res 1989;248:50. 23. Swanson KE, Stocks GW, Warren PD, et al. Does axial limb rotation affect the alignment measured in deformed limbs? Clin Orthop Relat Res 2000;371:246.
Please cite this article as: Davis JA, et al, Postoperative Coronal Alignment After Total Knee Arthroplasty: Does Tailoring the Femoral Valgus Cut Angle Really Matter?, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.03.013
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Postoperative Coronal Alignment After Total Knee Arthroplasty: Does Tailoring the Femoral Valgus Cut Angle Really Matter? Jason A. Davis, MD a, Craig Hogan, MD b, Michael Dayton, MD b a b
Ellis County Orthopaedics, HealthTexas Provider Network/Baylor Scott & White Health, Waxahachie, TX Department of Orthopedics, University of Colorado School of Medicine, Academic Office One, Aurora, CO
a r t i c l e
i n f o
Article history: Received 17 October 2014 Accepted 7 March 2015 Available online xxxx Keywords: Postoperative coronal alignment hip-to-ankle radiographs valgus cut angle total knee arthroplasty mechanical femorotibial angle
a b s t r a c t Postoperative alignment was measured in 80 TKA divided into 2 groups. Knees in the tailored group (n = 40) were performed with a personalized valgus cut angle (VCA) based on preoperative hip-to-ankle (HTA) radiographs. The fixed group knees (n = 40) were performed utilizing a 4° VCA in valgus knees and obese patients, and 5° in neutral and varus knees. There was no significant difference between groups in average preoperative mechanical alignment or average severity of preoperative deformity. There was no statistically significant difference between groups in postoperative mechanical alignment (tailored: 2.6°; fixed: 1.3°; P = 0.08) or severity of residual deformity (tailored: 3.5°; fixed: 2.6°; P = 0.10). Accuracy of the tibial cut angle (TCA) and severity of the preoperative deformity were strong independent predictors of postoperative alignment (R2 = 58% and R2 = 33%, respectively). © 2015 Elsevier Inc. All rights reserved.
Background In addition to soft tissue balancing and stable component fixation, implant alignment is arguably the most important technical factor for successful outcome and longevity in total knee arthroplasty (TKA) [1–5]. Many studies have implicated component malalignment in the failure of TKA through polyethylene wear and loosening [1,6–11]. Despite recent data challenging the ideal postoperative coronal alignment of the lower extremity [12–14], the most commonly accepted goal is to achieve a mechanical femorotibial (MFT) angle within + 3° of neutral such that the mechanical axis passes through the center of the knee in the coronal plane in effort to disperse forces across the implants in an even distribution. This is achieved by making coronal bone cuts perpendicular to the mechanical axes of the femur and tibia [1,3,5,8,11]. In regard to the femur, this cut is often referenced from the anatomic axis of the femur utilizing a corrective valgus cut angle (VCA) as there is a disparity between the mechanical and anatomic axes ranging from 2° to 9° with a mean of 5° to 6° along with some reported morphologic and gender variation [15–17]. Standard practice for many surgeons is to use the same VCA, typically 5° or 6°, for all patients with disregard for any variation in the femoral mechanical One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2015.03.013. The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2015.03.013. Reprint requests: Jason A. Davis, MD, Ellis County Orthopaedics, 2460 N. I-35 East, Ste. 225, Waxahachie, TX 75165.
anatomic (FMA) angle within the population. On the other hand, some surgeons tailor the intraoperative VCA based on preoperative standing hip-to-ankle (HTA) anteroposterior radiographs (Fig. 1), which have been shown to allow accurate measurement of alignment with strong interobserver and intraobserver reliability [18,19]. Controversy exists as to whether acceptable coronal mechanical alignment can be achieved by utilizing a standardized distal femoral VCA of 4° to 7° instead of a patient-specific VCA based on the FMA angle measured on preoperative HTA radiographs. The purpose of this study was to assess whether there is any significant difference in postoperative alignment between these 2 approaches by retrospectively comparing TKA performed by 2 surgeons who adhere to one or the other philosophy. We hypothesized that there would be no significant difference in the postoperative MFT angle or in the number of limbs that achieved alignment within + 3° of neutral with either approach in uncomplicated primary TKA. Materials & Methods After approval from the institutional review board, we performed a retrospective review of 80 primary TKA with appropriate radiographic records performed at a single academic institution from January 2013 to January 2014 by 1 of 2 fellowship trained total joint surgeons or by a fellow or resident under their direct supervision. All patients underwent cemented, posterior stabilized TKA. Patients were divided into 2 groups based upon which surgeon performed the procedure. Both surgeons utilize an intramedullary femoral guide for establishing the distal femoral cut, and an extramedullary guide to establish the tibial cut. The senior author utilizes gap balanced resection and determines the femoral VCA based on preoperative measurement on HTA
http://dx.doi.org/10.1016/j.arth.2015.03.013 0883-5403/© 2015 Elsevier Inc. All rights reserved.
Please cite this article as: Davis JA, et al, Postoperative Coronal Alignment After Total Knee Arthroplasty: Does Tailoring the Femoral Valgus Cut Angle Really Matter?, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.03.013
2
J.A. Davis et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx
institution by a single investigator (JD). All measurements were obtained from standing HTA radiographs. Preoperative alignment was determined by measuring the angle between a line extending from the center of the femoral head to the deepest part of the trochlea of the distal femur, and a line extending from the center of the proximal tibia as the midpoint between the tibial eminences to the center of the talus. Postoperative alignment was assessed by measuring the angle between a line extending from the center of the femoral head to the center of the cam and post articulation, and a line from the same to the center of the talus (Fig. 2). Each alignment measurement was performed 3 times by the same investigator with positive values representing varus alignment and negative values representing valgus alignment. Similarly, the angle of the tibial cut (TCA) was obtained by a single measurement utilizing a line from the center of the talus to the center of the tibial baseplate, and a line parallel to the tibial baseplate (Fig. 3).
Fig. 1. Determining the valgus cut angle (VCA) is performed by (A) identifying the femoral mechanical anatomic (FMA) angle formed by the angle between the anatomic axis of the femur (AAF) and the mechanical axis of the femur (MAF), then (B) applying the FMA angle to the perpendicular axis of the AAF.
radiographs (tailored group, n = 40). Tailored group knees were implanted with either the Journey II (Smith & Nephew, Inc., Andover, MA; n = 34) or the Sigma RP (Depuy,Warsaw, IN; n=6). Conversely, fixed group patients (n = 40) were performed by a surgeon who utilizes a measured resection and does not rely on preoperative HTA radiographic measurements to set the VCA. Rather, a fixed VCA of 5° is utilized for neutral or varus knees, and 4° is utilized for valgus knees or in obese patients with large medial thigh folds in an effort to avoid irritation during gait postoperatively. Knees in the fixed group were implanted with either the PFC Sigma (Depuy, Warsaw, IN; n=29) or the Attune (Depuy, Warsaw, IN; n = 11). Exclusion criteria were patients who underwent revision total knee arthroplasty, patients in the tailored group who did not have preoperative HTA films indicating that the VCA could not have been personalized, and patients who lacked postoperative HTA radiographs. Preoperative and postoperative mechanical alignment (MFT angle) as well as the angle of the tibial cut in each group were measured utilizing the digital PACS software (McKesson Radiology Station Lite) at our
Fig. 2. Preoperative and postoperative alignment of the lower limb is obtained by measuring the mechanical femorotibial (MFT) angle in (A) a preoperative hip-to-ankle (HTA) radiograph as the angle between the mechanical axis of the femur (MAF) and the mechanical axis of the tibia (MAT), and in (B) a postoperative HTA radiograph, respectively.
Please cite this article as: Davis JA, et al, Postoperative Coronal Alignment After Total Knee Arthroplasty: Does Tailoring the Femoral Valgus Cut Angle Really Matter?, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.03.013
J.A. Davis et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx
Fig. 3. The tibial cut angle (TCA) is measured by the angle between a line extending from the center of the tibial base plate to the center of the talus and a line parallel to the base plate. In this example, the angle is 91.8° or 1.8° of valgus.
Other data such as height, weight, body mass index (BMI) and type of implants were collected from the patients’ electronic medical records (preoperative history and physical notes and operative notes). Statistical Analysis The primary outcome measure was postoperative alignment. Two common transformations, the absolute value of the angle and an indicator for whether the angle was within + 3° of neutral, were also evaluated. Differences in continuous variables between the fixed and tailored groups were evaluated using 2-group t tests. A chi-square test for difference in proportions was used to estimate between-group differences in binary variables. Simple linear regression was used to evaluate the association between postoperative alignment (MFT angle) and preoperative alignment (MFT angle) and the association between postoperative alignment (MFT angle) and TCA. Multiple regression was used to estimate the combined effect of TCA and preoperative alignment. Intraobserver reliability was assessed using the intra-class correlation coefficient (ICC) by utilizing the Strout-Fleiss reliability statistic for repeated measurements. All analyses were done with SAS v9.3 (SAS Institute, Inc., Cary, NC). Results Intraobserver reliability showed a high level of repeatability in the measurement of preoperative and postoperative MFT angles on HTA radiographs. The ICC was 0.90 preoperatively and 0.96 postoperatively.
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There were no significant differences between study groups in regard to height, weight, BMI, average preoperative alignment or severity of deformity. Preoperative HTA radiographs were not available in 5 of the 40 patients in the fixed group. The average preoperative alignment (MFT angle) in the tailored group was 4.6° and the average MFT angle in the fixed group was 3.8° (P = 0.65). The average severity of deformity extrapolated by utilizing the absolute value of the MFT angle (representing the degrees deviation from neutral) was 6.9° in the tailored group and 7.2° in the fixed group (P = 0.75) (Table 1). The only difference between surgeons involved the TCA. The mean TCA in the fixed group was closer to 0°, averaging −0.6°, compared to 1.2° in the tailored group (P b 0.001). However, there was no significant difference between groups in the mean of the absolute values of the TCA (tailored: 1.9°; fixed: 1.8°; P = 0.70), a stronger indicator for the accuracy of the tibial cut (Table 2). Postoperatively, there were no statistically significant differences between study groups in alignment, severity of residual deformity, or the number of knees within + 3° of neutral. Given 40 knees per group, a difference of 1.5 in the average postoperative angle would have been significant at the 0.05 level; this difference is substantially less than 3̊, a difference that would be considered a clinically meaningful difference. The tailored group had an average postoperative alignment (MFT angle) of 2.6° and the fixed group had an average of 1.3° (P = 0.08). The tailored group had an average severity of residual deformity of 3.5° compared to 2.6° in the fixed group (P = 0.10). Twenty-two knees in the tailored group and 27 knees in the fixed group had postoperative MFT angles within + 3° (P = 0.25) (Table 2). Both the preoperative MFT angle (R2 = 33%) and TCA (R 2 = 58%) were independent predictors for postoperative alignment (MFT angle), and the preoperative severity of deformity (defined by the mean of the absolute values of the MFT angle) and accuracy of the TCA (defined by mean of the absolute values of the TCA) were independent variables impacting the postoperative residual deformity (defined by mean of the absolute values of the postoperative MFT angle). The strongest independent predictor was the TCA, and when combined with the preoperative MFT angle in a regression model, the R2 improved significantly (R2 = 66%). Discussion Currently, there is limited and conflicting data in the literature to determine whether there is an advantage in tailoring the VCA to each patient’s preoperative HTA radiograph. In a radiographic study of preoperative HTA radiographs by Bardakos et al, the VCA in 174 knees undergoing TKA was measured and determined that as many as 51% of patients required a VCA less than 5° or greater than 6° to achieve neutral alignment. The authors concluded that mechanical axis cannot be consistently restored utilizing a fixed VCA for all patients [15]. In a similar retrospective study of preoperative CT scout films of osteoarthritic knees in 83 patients, Kharwadkar et al found that the average VCA was 5.4°. Although the authors concluded that routine use of 5° or 6° for VCA is safe for uncomplicated primary TKA, Bardakos et al points out that despite leading to acceptable alignment on average,
Table 1 Preoperative Patient Indices as Mean. Tailored Group n Height (cm) Weight (kg) BMI (kg/m2) MFT angle (°) (ABS) MFT angle (°)
40 166 + 9.8 83.1 + 18.7 30.3 + 6.3 4.6 + 6.7 6.9 + 4.2
Fixed Group
P
a
40 170 + 11.1 85.0 + 21.9 29.3 + 5.3 3.8 + 8.1 7.2 + 5.2
0.10 0.69 0.41 0.65 0.75
BMI = body mass index, MFT angle = mechanical femorotibial angle, ABS = absolute value. Data are presented as mean + SD. a Preoperative radiographs were not available in 5 patients.
Please cite this article as: Davis JA, et al, Postoperative Coronal Alignment After Total Knee Arthroplasty: Does Tailoring the Femoral Valgus Cut Angle Really Matter?, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.03.013
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J.A. Davis et al. / The Journal of Arthroplasty xxx (2015) xxx–xxx
Table 2 Postoperative Radiographic Measurements as Mean.
n TCA (°) (ABS) TCA (°) MFT angle (°) (ABS) MFT angle (°) MFT angle + 3°
Tailored Group
Fixed Group
P
40 1.2 + 2.1 1.9 + 1.5 2.6 + 3.4 3.5 + 2.7 22 (55%)
40 −0.6 + 2.1 1.8 + 1.2 1.3 + 3.2 2.6 + 1.9 27 (68%)
b0.001 0.70 0.08 0.10 0.25
TCA = tibial cut angle, ABS = absolute value, MFT angle = mechanical femorotibial angle. Data are presented as mean + SD or N (%).
the data suggests 42% of the knees in the aforementioned study fell outside the 5° to 6° range; thus, a routine cut of 5° or 6° may lead to inaccuracy in a significant percentage of knees [15,20]. On the other hand, in 124 primary TKA, the use of preoperative HTA radiographs and a tailored VCA compared to a fixed 5° VCA failed to show a significant difference in the postoperative mechanical alignment in a single-surgeon, prospective randomized study by McGrory et al when using the central 1/3 of the knee to define neutral alignment. There was also no difference between groups in postoperative mechanical alignment by average distance from neutral. Patients with previous hip or ankle surgery, femoral or tibial fracture, deformity of 15° or greater, or those with a BMI N 40 kg/m2 were excluded [21]. Most recently, Deakin and Sarungi published a single-surgeon retrospective cohort study of 124 knees performed with a fixed 7° VCA compared to 87 knees performed with a variable VCA based on preoperative HTA radiographs. Eighty-five percent of knees in the variable group had postoperative alignment within + 3° of neutral compared to 69% in the fixed angle group, a statistically significant difference (P = 0.006). The authors concluded that a fixed VCA is inappropriate and that tailoring the VCA to the patient’s specific anatomy can improve postoperative alignment [19]. It should be noted that the importance of obtaining a mechanical axis within + 3° of neutral has recently been called into question. Parrette et al published the results of a 15 year retrospective survivalship study of 398 knees. In the so called mechanically aligned group of 292 knees, there were 45 (15.4%) revisions compared to 14 (13%) of the 106 knees with mechanical alignment outside + 3° of neutral (P = 0.88). Seventeen (5.8%) of the 292 implants in the mechanically aligned group were revised for aseptic loosening, mechanical failure, or wear, compared to 4 (3.8%) of the 106 implants outside the acceptable range (P = 0.49). The authors concluded that postoperative mechanical alignment of 0° + 3° did not improve 15 year survival and showed little predictive value [12]. In a different 15 year follow-up study, Bonner et al showed similar results, although the authors do mention a statistically insignificant trend that favors knees that are more accurately aligned [13]. Furthermore, the concept of so called “constitutional varus” has been demonstrated by Bellemens et al in the normal population, and the authors suggest that a neutrally aligned total knee implant for these individuals may not be natural or desirable [14]. Despite these recent challenges, achieving a neutral alignment after TKA is the most widely accepted surgical goal emphasized in the literature. In this study, we demonstrated that there was no statistically significant difference, and more importantly, no clinically meaningful difference, in postoperative mechanical alignment between TKA performed by a surgeon who customizes the VCA based on the FMA angle measured on preoperative HTA radiographs, compared to a surgeon who utilizes a standardized VCA of 4° for valgus knees and obese patients, and 5° for neutral or varus knees. The results were consistent across 3 commonly utilized methods in the literature: evaluating the mean alignment where varus and valgus are designated with a + or − value; evaluating the mean of the absolute values of alignment to demonstrate the mean distance from neutral, or in other words, the average severity of the coronal plane deformity; and presenting the number of knees that fall within or outside the generally accepted + 3° of
neutral [4]. The results also demonstrate that the accuracy of the tibial cut (TCA) and the severity of the preoperative deformity (MFT angle) are strong independent predictors of postoperative alignment. Thus, the importance of achieving an accurate tibial cut perpendicular to the mechanical axis of the tibia becomes significantly more important as the severity of the preoperative deformity increases. The current study has a number of limitations. Due to the retrospective nature of this study, there were several patients not included in the study due to incomplete radiographic records. Also, there was no standardized protocol which introduces subjectivity in establishing the VCA as well as selection bias. Furthermore, the study groups were defined by 2 different surgeons, each with trainee involvement, which introduces several potentially confounding factors. First, the differences in skill and intricacies in surgical approach are not standardized to each group. However, despite a gap balanced versus measured resection, both surgeons perform the distal femoral and proximal tibial cuts in like fashion with an intramedullary femoral guide and an extramedullary tibial guide, respectively. Thus, whether a gap balanced or measured resection was utilized, there should have been no bearing on establishment of the coronal alignment in extension between surgeons. In addition, the fact that multiple implant systems were used in each group raises the question of whether disparities exist between the instrumentation and what effect that may have on the accuracy, consistency and orientation of both the distal femoral and proximal tibial cuts. Although the current study was not designed to evaluate this variable, in the small sample available there was no evidence that choice of instrumentation made an impact on postoperative coronal alignment. Nevertheless, a prospective, randomized, single-surgeon, singleimplant study would be the optimal design to eliminate these potentially confounding factors for future studies. Other limitations to consider are those associated with the assumption of HTA radiographs as an accurate representation of true alignment. It has been demonstrated that with 40° of limb rotation, the femoral mechanical anatomic (FMA) angle can vary by 1° to 2.5° and the limb alignment (MFT angle) can vary up to 5° [22,23]. Thus, without a standardized protocol for obtaining HTA (same stance, limb rotation, distance from x-ray source, technician, etc.), there is risk for error. Conclusions Despite the limitations of this study, our data suggest that when performing an uncomplicated primary total knee arthroplasty, utilizing a standardized VCA of 4° for valgus knees and 5° for neutral or varus knees can lead to acceptable postoperative alignment. The severity of the preoperative coronal deformity and the accuracy of the tibial cut are strongly correlated to postoperative alignment, and imply that achieving a tibial cut perpendicular to the mechanical axis of the tibia becomes particularly more important as the severity of the preoperative varus or valgus deformity increases. Acknowledgments The authors thank Pamela Wolfe, PhD, for her time, effort, and expert statistical analyses. The authors affirm there was no outside funding or industry influence for this study. References 1. Jeffery RS, Morris RW, Denham RA. Coronal alignment after total knee replacement. J Bone Joint Surg (Br) 1991;73(5):709. 2. Matsuda S, Kawahara S, Okazaki K, et al. Postoperative alignment and ROM affect patient satisfaction after TKA knee. Clin Orthop Relat Res 2013;471(1):127. 3. Longstaff LM, Sloan K, Stamp N, et al. Good alignment after total knee arthroplasty leads to faster rehabilitation and better function. J Arthroplasty 2009;24(4):570. 4. Rebal BA, Babatunde OM, Lee JH, et al. Imageless computer navigation in total knee arthroplasty provides superior short term functional outcomes: a meta-analysis. J Arthroplasty 2014;29(5):938.
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Please cite this article as: Davis JA, et al, Postoperative Coronal Alignment After Total Knee Arthroplasty: Does Tailoring the Femoral Valgus Cut Angle Really Matter?, J Arthroplasty (2015), http://dx.doi.org/10.1016/j.arth.2015.03.013
